ACP Workbench + REW

Hi all!

Just wanted to share my experience with REW and ACP workbench! Before I get started I want to inform everyone that I am not a audio guru and have learned most of what I know from YouTube… so if you have any suggestions or comments I’d be glad to hear them!

If you don’t know about ACP Workbench… it is 20 bucks and does all sorts of EQ and other neat sound processing things for UP2Stream boards. I just bought it and wanted to share my experience using the Up2Stream mini and the free software Room EQ Wizard (REW), to do some eq on the speakers in my room.

I begun this by using the UMIK-1 calibrated microphone and ran a couple frequency sweeps from my speakers. If you don’t know how to do this check out this link: Correct your speakers with REW, UMIK-1 and Equalizer APO (Room Correction Tutorial) - YouTube

Then I used REW’s Auto EQ settings to generate some filters for my speakers. Now this is where things get a bit interesting. The ACPWorkbench only has the ability to do 10 filters and REW spits out 20 filter suggestions. Since I wanted an accurate calibration I didn’t want to have to use only 10 filters and wanted to use the full 20 output by REW. Fortunately there is a way around this, to do it you have to break it up into two different filter sections, one in the main eq and the other in the Left/ right/ mono areas. (check out pictures below)

Since ACPWorkbench doesn’t have the ability to load in a text file (which they should totally add…) the next step is to enter the filters 10 frequency values from REW into the main EQ in ACPWorkbench and then the next 10 into the Left/Right/Mono EQ area, once that’s done you’re all set!

Just don’t forget to write it to your board! For only 20 bucks the ACPWorkbench is a great way to improve the quality of your speakers giving you DSP that would cost $50+ to buy it on your own (plus you can use it on multiple boards). Hope that was helpful.

Before I end this I want to give a couple suggestions for features that would be useful for ACPWorkbench. The first is adding 20 filters to your main EQ, since it would be useful to reserve the L+R channels for other eqing. In addition to that allowing text file uploads would also be helpful. Also having a way to write a couple different eq settings to the app would be nice. Finally, for my purpose I am looking to dynamically adjust the EQ based on the system volume. I have a couple speakers that are bass limited and want to boost the bass at low volume and then reduce it at high volume ( if I try to turn the bass up at high volumes my speakers sound like crap - Don’t ask). If there was a way to turn that bass down at high volumes that would be awesome. Overall though I was super impressed, and look forward to seeing what other awesome features they come out with!


Very impressive, and thanks for the sharing, it’s a good reference for audio calibration. Since the product is not so intellegent yet, we still can do it manually :slight_smile: . But take care for the gain, it’s too large for some frequencies in my comprehending, and music will have distortion when set bigger volume, better apply a negative pregain instead of +2dB.

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Glad you enjoyed! And thank you for the feedback… I am trying to learn more about gain eq and DSP and so if you know a good place to look I would appreciate it!

Hi Will,
Thanks for sharing your experience :+1:. I did the same a couple of days ago for my newly-built boombox, except that I used REW only for measurement and tweaked the filters in ACP Workbench by hand. Discovered the filter generation in REW only afterwards :woozy_face:.

One noob question: Did you find a detailed description of the filter types ACP Workbench provides? On the UI, they only show graphic icons instead of filter names and it is hard for me to figure out what does what. I can identify lowpass and highpass from the icons but some of the other icons are not clear to me.

Regards, Sven

Hi Sven,

Ooo interesting, how did you get ACPWorkbench and REQ to sync up? I was trying to evaluate my frequency response after I applied the filters but couldn’t figure that part out.

It looks like if you click the dropdown arrow to choose filter type and then hover over a filter icon the type will come up after about a second. But if that doesn’t work the filters are as follows from top to bottom: Peaking, Low Shelf, High Shelf, Low Pass, High Pass, Band Pass, and Notch. Hope that helps!

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Hi Will,

Thanks for the fast reply. Yes, this helps a lot. Maybe I was too busy moving my mouse around to give the tooltip a chance to appear :wink:. Will try to be more patient next time.

In my setup, REW and ACPWorkbench did not really sync up, at least not automatically. I did an initial full-range measurement with REW, analyzed the resulting frequency response, added some filters in ACPWorkbench, transmitted the settings to the Arylic amp, did another measurement with REW, checked whether it had changed to the better or worse, tweaked the filter settings or added new filters, etc. This took me about two hours and then the response looked acceptable (and my ears started bleeding) I called it a day. I ended up with six filters for the overall equalizer (all Peaking), three filters for the mid-high speakers (Highpass + Peaking) and seven filters for the subwoofer (Lowpass + Peaking). The frequency response is still a bit too turbulent for my taste but I will redo the process not before I have learned a bit more about speaker tuning.

Ahh Gotcha… I am using the Up2Stream Mini and running REW on the computer ( it doesn’t have a aux in) so I was doing frequency response through my amp instead of the Up2Stream. But I just realized that the USB port works for connecting REW as well. I’m glad to have this thread goin, hopefully we all can learn a little more about how to use this pretty sweet program!

Hi will, I did not learn in system and can’t give you any materials in further. And I just tried to understand the processing of audio signal for input, processing and output. Maybe I try to explain what I understood and hope it would explain a bit.

As you can see in the image for EQ curves, when add a positive gain on one frequency point, that means the audio output of the specific frequency will have more power than the input. But in digital processing, the maximum volume is 1.0(normalized, 32768 for 16bits audio), or called 0dB, which means input a sine wave varies from -1 to +1, and with no gain and decay, output a sine wave varies from -1 to +1 without any distortion. And if the audio sample has value 32768 and you want more, sorry the 16bits data can’t hold it and which means it will be cut or overt flow. So the volume can’t exceed 0dB for digital audio.

And you can consider the classD amp, when PVDD is supplied, the max voltage of the output audio wave will not exceed the PVDD, and if you try to increase the volume (or gain) more and more and exceeds a threshold, the output will have distortion, in the audio wave you would see the top or bottom of the signal is cut.

So come back to the EQ you’ve applied to the up2stream system, you’ve applied a +10dB gain on some frequencies, and with a +2dB pregain, so the max gain will be +12 dB, and as you would have understand, the volume of digital audio can’t exceed 0dB, and the part which exceeded will be cut and cause distortion. So you should set the pregain to -10dB to process audio signal safely.

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